The invention relates to a rotary-wing aircraft rotor whose blades are, at least some of them, foldable and equipped with an electrical device requiring the transfer of electrical energy or signals between the blades and an electrical collector placed at the centre of the hub of the rotor, for example a de-icing device requiring routing of electrical energy to the blades from the collector. This transfer of electrical energy or signal is provided by an electrical connection installation, essentially comprising, for each blade, at least one electrical connecting cable, tied to a member for linking the corresponding blade to the hub of the rotor, and provided at its ends with connectors to ensure an electrical connection between the collector and the blade.
More precisely, the invention relates to a rotary-wing aircraft rotor, in particular a helicopter main rotor, of the type known in particular by EP-0 754 623 and FR 2 781 198 and comprising:
a hub, designed to be driven in rotation about an axis of the hub which is the axis of rotation of the rotor,
at least two blades, each of which is connected to the hub by a link member that is substantially radial with respect to the axis of rotation, and a radially outer end of which is shaped as a fork in which the corresponding blade has a root retained by two substantially mutually parallel blade pins each passing through aligned bores in the fork and the blade root and each retained on the fork by at least one first removable retaining member, at least one blade being foldable on one side of the rotary-wing aircraft and having at least one removable blade pin so that removal of said removable pin from the blade root and from the fork of the link member, after removal of said at least first removable retaining member holding said removable blade pin on said fork, allows the blade to pivot about the other pin which forms a blade pivot pin, and
an electrical connection installation comprising, for each blade, at least one electrical connecting cable connecting a first connector, carried by the hub and electrically connected on the latter, to a second connector on the blade and connected to at least one electrical device of said blade, for example a de-icing or anti-icing device.
On a rotor according to EP 0 754 623, the connecting cable, for at least one manually foldable blade, comprises a first section, radially towards the outside, arranged like an overhead hook extending from this blade to the corresponding link member, and connecting the second connector on this blade to a first end, in a radially outer position, of a second section of connecting cable, held substantially radially on this link member. This overhead hook of the connecting cable has a rounded cross section, possibly an armoured structure, and is connected to a pin connector of the second connector, which pin connector is connected to the socket of this second connector, this socket being fixed to the blade and connected to the electrical device of this blade.
During the foldings of the blade, the pivoting of the blade in the outer radial fork of the corresponding link member may introduce tensions that can damage the overhead hook and the second section of the connecting cable and the second connector, and/or this overhead hook may oppose complete folding of the blade.
In order to remedy this disadvantage, EP 0 754 623 makes provision for the pin connector of the second connector, on the corresponding end of the overhead hook of the connecting bale, to be connected removabley to the socket of the second connector, which is fixed to the blade. In fact, it is not recommended to give this overhead hook a length sufficient to allow the complete folding of the blade without disconnecting this connector, because an overhead hook of such length would have large forces applied to it and would be subjected to ample flutter movements, favouring its unwanted catching on or collision with adjacent components, such as blade root pendular anti-vibration devices or drag dampers, on a rotor in rotation, on which the corresponding blade carries out angular deflections in pitch, flapping and drag.
In consequence, if there is a desire to maintain the advantages afforded by the other characteristics of the connection installation described in EP 0 754 623, to which reference may advantageously be made for further details, it is not possible to avoid manual disconnection and connection between the pin connector and the socket of the second connector in the event of manual folding and unfolding (or deployment) of the blades, before folding and after returning a blade to the flight configuration, respectively.
FR 2 781 198 proposes improvements to rotors with foldable blades and an electrical de-icing installation according to EP 0 754 623, in particular for reducing the stresses and/or displacements of the connecting cable in its overhead hook section connecting the link member to the second connector on the blade, when the rotor is rotating and during the operations of folding and unfolding the blades.
For this purpose, according to FR 2 781 198, an elongated part of this overhead hook, of substantially flattened rectangular cross section, whose largest dimension is oriented substantially parallel with the axis of rotation of the rotor, is held in a member, mounted in a fixed manner or pivoting about the folding spindle, in the substantially axial projection of this folding spindle, and arranged as a fork in which the said elongated part of flattened cross section is engaged and held by at least one elastic tab. This retaining fork prevents the displacements of the overhead hook on either side of the folding spindle, during a blade""s folding or unfolding, which prevents torsions harmful to this section of connecting cable, and it is no longer necessary to disconnect the connection between the overhead hook and the de-icing device at the second connector before folding the blade, provided the length of this overhead hook is sufficient without being so great as to give rise to the aforementioned disadvantages (whipping and snagging).
But the flattened rectangular cross section of this overhead hook section of cable above the link between the blade root and the link member may generate a certain amount of aerodynamic drag, and cause a disturbing slipstream phenomenon. Furthermore, considering the angular movements, in particular of flapping, of this section of cable and of its mechanical link with the link member, when that latter and the blade are carrying out these angular movements, it has proved necessary to form recesses in the periphery of a profiled dome covering the rotor head, and this amplifies the said slipstream phenomenon.
The basic problem for the invention is to overcome these disadvantages whilst avoiding the disconnection between the connecting cable and the second connector on the blade, for folding of the latter, and avoiding the formation of a disturbing slipstream, caused by recesses in the profiled dome surmounting the rotor head and by a section of connecting cable with a flat profile oriented substantially parallel with the axis of the rotor.
For this purpose, the rotary-wing aircraft rotor according to the invention, of the type described above, is characterized in that the connecting cable, for at least one foldable blade, comprises a first flexible section, of essentially cylindrical shape with a rounded cross section, preferably substantially circular, connecting the said second connector to a second section, held on the corresponding link member, of the said connecting cable, whose first section comprises a releasable part which, when the blade is in the flight configuration, is held above the said pivot pin by retaining means which are linked to the pivot pin and arranged in such a way that the releasable part of the first section of cable is manually releasable from the said retaining means, the said releasable part being manually released from the said retaining means before the said removable blade pin is removed, so that once the said removable blade pin has been removed, the folding of the blade by pivoting about the said pivot pin causes the first section of cable to curve and move naturally in order to accommodate the said folding without disconnecting at the second connector.
Advantageously, in a simple form of embodiment, the retaining means comprise a cradle, formed in a cable support and in which the said releasable part is retained by at least one collar articulated to one edge of the cradle and which can be folded down into the closed position onto the opposite edge of the cradle, to which the collar is intended to be fixed detachably, by at least one detachable retaining element, in a position of holding the said releasable part between the cradle and the collar, the said cable support being linked to the said pivot pin in such a way that after the said detachable retaining element has been detached and the said collar has been opened, the releasable part of the said first section of cable can be manually released from the cradle and from the said collar before the blade is folded.
The rounded shape of the cross section of the first section of cable sets up only a limited aerodynamic drag and allows, at the level of the connection with the second section of cable, a fixing much closer to the link member, such that it is no longer necessary to form recesses in a protective dome of the rotor head. Furthermore, no matter on which side of the helicopter the folding of a blade is carried out, the first section of connecting cable is held, when the blade is in the flight configuration, by its releasable part and by the intermediary of the collar and the cable support cradle, on that one of the two blade pins which constitutes the pivot pin for folding, so that once this section of cable has been manually released from the cradle and from the collar and the removable blade pin has been removed, this section of cable is completely free between the second connector, on the blade, and the second section of cable, on the link member, and can deform naturally, particularly can curve and move, so as to follow the blade in its folding without exerting damaging tension on the second connector which thus need not be disconnected.
Advantageously, the cable support is a support spindle engaged in the blade pivot pin, which is tubular, substantially along the axis thereof, and retained in substantially axial translation in the said pivot pin by at least one second removable retaining member.
In this case, according to an advantageously simple and economical arrangement, the cradle is formed in the upper end of the said support spindle which projects above the said blade pivot pin.
The second removable retaining member can comprise at least one safety pin intended to pass transversely through the support spindle and the blade pivot pin in their lower ends projecting under the fork of the corresponding link member so as to axially and rotationally retain the support spindle in the said blade pivot pin, and it is then advantageous for this safety pin at the same time to constitute the said first removable retaining member intended to retain the blade pivot pin in the position of retaining the blade root in the said fork, when the corresponding blade is in the flight configuration. Thus, if one or two spring pins is or are used to lock the blade pivot pin to the fork, when the blade is in the flight configuration, this or these spring pin(s) at the same time retains or retain the cable support spindle in the blade pivot pin.
Advantageously, the support spindle is retained in the blade pivot pin with a small axial clearance by the said safety pin bearing against a washer made of a synthetic material, preferably polyurethane, which surrounds the lower ends of the support spindle and of the pivot pin projecting under the fork and which comes into abutment against the underside of the fork.
In an advantageously simple embodiment, the detachable retaining element comprises at least one removable connecting pin connecting the collar and the support spindle and intended to keep the collar closed onto the cradle so as to keep the said releasable part in the cradle.
In an advantageously simple and economic embodiment, the collar is articulated with pivoting, substantially by one of its ends, about a bolt mounted laterally on the cradle substantially parallel to part of the removable connecting pin which passes through aligned bores in an opposite lateral part of the cradle and in the other end of the collar when the collar is in the closed position, which, projecting, carries a protrusion which, in flight, limits the movements of the removable connecting pin.
Also advantageously, as known from EP 0 754 623 and FR 2 781 198, and for the reasons given in these two documents, the second section of cable has an elongated part extending substantially radially and of substantially flattened rectangular cross section, maintained substantially flat on the top of the said link member, that is to say such that the largest dimension of its cross section is oriented substantially perpendicular to the axis of the rotor, in particular in order to facilitate the fixing of this second section of cable on the link member, to reduce the aerodynamic drag and to attenuate the mechanical forces applied to this section of cable.
Thus, the rotor according to the invention can also benefit from the advantages resulting from the use of other features of the electrical connection installation according to EP 0 754 623 and FR 2 781 198, to which reference can be made for more details, and the specifications of which are incorporated in the present specification by way of reference.
In particular, the second section of cable can be advantageously connected to the first connector on the hub by the intermediary of a third section of the connecting cable, the said third section comprising an overhead hook, in the shape of a flattened half-loop, of substantially flattened rectangular cross section whose largest dimension is substantially perpendicular to the axis of rotation, and whose concavity is facing substantially towards holding and articulation means connecting the corresponding link member to the hub, and substantially radially towards the axis of rotation, the said overhead hook being thus deformable in flexion and torsion in order to accommodate itself to the angular deflections in pitch, drag and flapping of the blade and of its link member with respect to the hub, as known from the two documents mentioned above.
Similarly, the second section of cable can advantageously be connected to the overhead hook of the third section of cable by a joint connected to the link member by a link which is articulated at least in pivoting manner about an axis substantially parallel with or slightly inclined with respect to the longitudinal pitch change axis of the link member and of the blade, in order to attenuate the mechanical forces applied to the connecting cable whilst allowing a good take-up of the forces applied to the latter when the rotor rotates and the corresponding blade is carrying out its angular deflections in pitch, flapping and drag, as proposed in FR 2 781 198.